Knowledge of the weight of an aircraft is crucial for its operation, and safety. Knowledge of the weight allows the calculation of the maximum payload that can be transported a known distance and the amount of fuel required. Knowledge of the point of balance or center of gravity (CG) of an aircraft is also important. For example, if the longitudinal CG is located too forward, the aircraft will be nose heavy, if located too aft, tail heavy. A tail heavy aircraft that deviates from the recommended tolerances may become hazardously unstable exhibiting uncharacteristic spin and stall characteristics. Prior art methods for determining the weight of an aircraft include the use of aviation scales, and weighing sensors located in the landing gear, particularly in the main and nose wheels axles. Each of these prior art methods has its own disadvantages. The main function of the landing gear is not only to support the weight of the aircraft on the ground, but also to at least partly dissipate the tremendous amount of energy produced during the landing impact. Weighing sensors located in the landing gear, and especially the wheel axles are affected by changing conditions that include mechanical factors (e.g., damping pressure, tire pressure, vertical elasticity of the tire, material fatigue, etc.), environmental factors (e.g., temperature, humidity, corrosion, contaminants, etc.), variability in periodic maintenance and service, and the like. Hence, these regular changing conditions may hamper the reliability, accuracy, and efficacy of weight assessment.
The relationship between weight and balance of an aircraft and its safety is recognized and documented. For example, an article entitled “Analysis of aircraft weight and balance related safety occurrences” published by the National Aerospace Laboratory (NLR) of the Netherlands, studies weight and balance related incidents (including accidents) of passenger as well as cargo aircraft. This study concludes that the accuracy and reliability of (then-known) prior art weight and balance systems are insufficient to impose their use as a primary means for determining aircraft weight and balance.
U.S. Pat. No. 8,235,326 B2, issued to Braincourt et al. and entitled “Aircraft Landing Gear Load Sensor” is directed at a fiber optic load sensing system and method for measuring load in an aircraft landing gear. The fiber optical load sensing system includes a plurality of Bragg Grating sensors written into a fiber optic cable, and an interrogator. The fiber optic cable is mounted, such that it is firmly clamped or bonded to the inside of an axle (right and/or left) of an aircraft landing gear. When the axle deflects under vertical and/or drag load, the optical fiber bends in sympathy. The interrogator determines the change in radius of the optical fiber caused by the bending. The change in geometry of the optical fiber is equated to the load that caused the deflection. A remote control and a recorder unit record the output of the fiber optic load sensing system. A plurality of load sensing measurements is taken corresponding to each wheel location such that the load apportionment and total load can be established for a wheel group of the aircraft.
PCT International Publication Number WO 2015/088967 A1 to Moog Inc., entitled “Fiber Optic Sensing and Control System” is directed at a fiber optic sensing aeronautical flight control system for air and space vehicles. The fiber optic sensing and control system includes sensing optical fibers, and an interrogator unit. The sensing optical fibers each include multiple fiber optic sensing points that are integrated or coupled to primary and secondary flight control surfaces of the aircraft. The so-called primary flight control surfaces of the aircraft (airlerons, elevators, and rudder) are used to control aircraft movement in the pitch, yaw, and roll axes, whereas the so-called secondary flight control surfaces (inboard and outboard spoilers, inbound and outbound flaps, flaperons, and slats), are used to influence the lift or drag of the aircraft. The optical fibers are connected to the interrogator unit. The flight surfaces of the aircraft exhibit aeroelastic effects as well as structural loads, as gusts of wind and other forces are applied thereto. The sensing optical fibers sense and measure deformations and oscillations caused by the structural loads. The interrogator interrogates the sensing optical fibers. A flight control computer of the aircraft analyzes the measurements, the analyzed results of which are then fed back to an actuator that controls its corresponding flight control surface.